Just what the header says. What's one of these BL thingies? They looks kinda
fun, but I'm not completely sure what's going on here.

You've probably received a hatful of answers already, but an Englishman
with the last name Bulwer-Lytton was one of the most popular writers of
the 19th century, but is primarily remembered today for churning out
pretty awful junk -- and the infamous opening line "It was a dark and
stormy night".  There is a contest here in the States named for him where
people submit one-paragraph openings for books -- the worst possible
openings for the most awful books possible -- and the worst of these
submitted in a given calendar year wins.  The entries are collected in a
series of books called (appropriately enough) "It Was A Dark And Stormy
Night", "Son of Dark and Stormy" and so on, which you may be able to find
in the humor section of any fair-sized bookstore. 

Here in the ML, the Bulwer-Lyttons are limited to the openings of truly
rancid fanfic concepts...